Dear PLS experts,

I have both working memory and episodic memory block designs from the same participants. I am interested to see which brain networks are commonly and/or uniquely engaged during the tasks, and also how such networks are correlated with performance and age. I guess the multi-block pls should be an optimal approach to address both questions simultaneously, right? If so, I have a couple of questions:

1. Given that age and performance are highly (anti) correlated, doesn’t that make a collinearity problem for the multiblock PLS?
2. Which correlation mode should I use? I have a pretty skewerd age range, such that there are only 50 subjects younger than 50 years old (age-range:25-50) but 275 subjects older than 55 (age range:55-80). Is it ok if I model age as a continuous variable?
3. Finally, I want to exemplify the way that I interpret the multiblock PLS findings to make sure that I am correct:

LV1: Task PLS part of the multiblock (Brain score): Con A Con B Con C: -38 -5 43

It is clear that this LV reflects those brain areas with greater activation during condition A&B (task) than condition C (baseline) and vice versa. Note that the sign for brain scores of the task conditions (A&B) are negative.

LV1:behavioral PLS part of multiblock:

Correlation between Brain scores of condition A and behavioral measure 1: r = - 0.38

Correlation between Brain scores of condition A and behavioral measure 2: r = 0.25

Given the sign of the voxel saliencies and also brain score for task conditions (A&B conditions) derived from task PLS are negative; I am just wondering whether I need to reverse the sign of the correlation between brain score of the task conditions and behavioral measure. On the other word, do you say that the voxels that are more activated during task (A&B) than baseline C (i.e. these regions have negative saliencies) are positively or negatively correlated with behavioral measure 1?

Thanks a lot for your help.

Best

Kami